1. Field of the Invention
The present invention relates to a signal converting apparatus comprising a D/A (digital-analog) converter and an A/D (analog-digital) converter.
2. Related Background Art
Hitherto, various related background arts have been known as such a kind of apparatus. As an example, a serial/parallel type A/D converter which is used in a system of a whole solid state camera is shown in FIG. 1 together with peripheral circuits. In the diagram, reference numeral 1 denotes a clamp circuit; 2 a sample and hold (S/H) circuit; 3a a serial/parallel type A/D (analog-digital) converter; and 4, 5a, 6, and 7 an A/D converter of the upper a bits parallel type, an a bits D/A (digital-analog) converter, a differential amplifier, and an A/D converter of the lower b bits parallel type which are component elements of the serial/parallel type A/D converter 3a, respectively. Reference numeral 8 denotes a digital signal processing circuit; 9 a memory circuit; and 5b an (a+b) bits D/A converter.
The operation will now be described.
An input video signal is processed by the clamp circuit 1 and the sample and hold circuit 2 and becomes the video signal adapted as an input signal of the serial/parallel type A/D converter 3a. The video signal is converted into the digital video signal by the A/D converter 3a. The A/D converter 3a comprises: the two A/D converters 4 and 7 of the parallel comparison type; the a bits D/A converter 5a; and the differential amplifier 6. The A/D converter 3a is the well-known typical serial/parallel type A/D converter. Since the a bits D/A converter 5a is concerned with an accuracy of the A/D converter 3a, an accuracy of (a+b) bits or more is obviously required for D/A converter 5a. The A/D converted digital video signal is subjected to a digital signal process such as an image encoding or the like by the DSP (digital signal processing) circuit 8, and thereafter, it is controlled by a write control signal and stored into the memory circuit 9.
The digital video signal which was controlled by a read control signal and was read out of the memory circuit 9 is subjected to a process such as an image decoding or the like which is opposite to the above process by the DSP circuit 8. After that, the processed digital video signal is converted into the analog video signal by the (a+b) bits D/A converter 5b and generated.
However, in the above conventional example, it is necessary to provide two highly accurate D/A converters 5a and 5b. There are problems when a plurality of sets each comprising the serial/parallel type A/D converter 3a and D/A converter 5b are integrated; for instance, it is disadvantageous from viewpoints of the chip size, electric power consumption, and costs.